The invention relates to suspended ceiling systems and, in particular, to improvements in grid structure for such systems.
Narrow-faced grid tees for supporting ceiling boards or tiles have desirable aesthetic properties but can present problems in properly supporting the tiles. Currently produced ceiling tile is difficult to manufacture with precise dimensions and is susceptible to dimensional changes due to variation in moisture content as a result of humidity changes. It is possible for a grid tee to deflect laterally far enough to allow the edge of a tile, generally in the area of the mid-length of the tee, to drop down below the plane of the grid. This condition is to be avoided since it presents an unacceptable appearance. U.S. Pat. No. 4,679,375 illustrates two alternative designs for centering a grid tee between adjacent tiles. While these designs improve the performance of narrow-faced grid systems, they fall short of a fully satisfactory solution to the problem. In one design of this patent, integral centering tabs are stamped out of the web of the grid tee. These integral centering tabs are prone to locally crush the edges of the tile during original installation or later when the tile is removed and reinstalled for access to the plenum above the ceiling. When the tabs crush or otherwise impale themselves into the tile, they lose their centering function and leave the system again susceptible for a tile edge to drop off a flange. The other embodiment or design of the patent comprehends separate spring clips that snap over the grid tees and provide laterally diverging resilient legs that are compressed by engagement with the edges of adjacent tiles. The separate clips are undesirable because of their added costs and the uncertainty of proper installation in the field.
The invention provides an improved narrow-faced grid tee for a suspension ceiling system that reduces the risk of improper alignment between the tee and the tiles it supports. The grid tee thus avoids the unsightly dropping of a tile edge off of a flange of a misaligned tee. In accordance with the invention, the grid tee is formed with integral centering tabs that by their special configuration exhibit a resilient or spring-like character. The spring action of the tabs allows them to accommodate large variations in the size of the tile without either impaling themselves into the tiles or permanently bending or deforming out of a zone where they are effective for centering purposes. The geometry of the tabs achieves a surprising degree of resilience despite the typically relatively soft non-springy mild steel composition of the body of the tee.
Preferably, the grid tee is manufactured by roll-forming mild steel strip stock into a conventional tee configuration with a vertical web formed by a double layer of this strip stock. The resilient tab of the invention in the illustrated embodiments is shear cut out of the web on three sides of the tab profile leaving it integrally attached to the web at a fourth side. In this circumstance, the tab functions like a double leaf spring enabling its free end to deflect a relatively large distance without exceeding the yield point of the material. The two parts or leaves of the tab operate together to provide twice the resistance force available from one leaf but with a resilient deflection potential substantially greater than what would be possible with thicker material stock.
Each tab, ideally, has a spoon-like free end so that its cut edges are set inwardly of the laterally outermost portions of the tab to thereby avoid cutting into the edges of the tile when the tile is being installed or removed. While the tabs are preferably formed on both sides of the web, they are sufficiently longitudinally displaced from one another to avoid transmitting the forces on one tab directly to the adjacent tab on the opposite side of the web. This independent action of the tabs allow for greater predictability and control of the spring performance of the tabs.
The invention has utility in various other suspended ceiling grid systems where it is important to precisely control the horizontal position of a tile relative to the tees. Examples of other applications are so-called concealed grid systems where there is typically only a narrow supporting portion of a tile overlying the tee flange. The widths of the faces of the tees in such systems can be full or narrow, but in either case it is important to precisely control the position of a tile on the grid to prevent it from slipping off a flange.